In a long term evolution (LTE) Rel-8/9/10 system, physical downlink control channel (PDCCH) is transmitted in each subframe, as shown in FIG. 1. It occupies first N orthogonal frequency division multiplexing (OFDM) symbols of a subframe, wherein N may be 1, 2, 3 or 4.
In the LTE Rel-8/9/10 system, a control area used for transmitting the PDCCH consists of logical control channel elements (CCEs), wherein one CCE consists of 9 RE groups (REG). One REG consists of 4 resource elements (REs) which are the same in the time domain and are adjacent in the frequency domain. The REs constituting the REG do not include those used for transmitting common reference signals. Detailed definition of the REG is as shown in FIG. 2.
Downlink control information (DCI) is also transmitted taking CCE as a transmission unit. For the DCI of a user equipment (UE, i.e., user terminal), it may be transmitted on M logically continuous CCEs. In the LTE system, the value of M may be 1, 2, 4 or 8, which is referred to as aggregation level. The UE performs a blind detection in the control area, determines whether there is PDCCH transmitted for the UE. The blind detection is to perform decoding attempts with respect to different DCI formats and CCE aggregation levels using radio network temporary identity (RNTI) of the UE. If the decoding is correct, the DCI with respect to the UE is received. The LTE UE needs to perform the blind detection in the control area of each downlink subframe in a discontinuous reception (DRX) status and searches for the PDCCH.
FIGS. 3a, 3b and 3c show configurations of channel state information-reference signal (CSI-RS) in an LTE Rel-10 system, wherein FIG. 3a shows the configuration for 2 ports, FIG. 3b shows the configuration for 4 ports, and FIG. 3c shows multiplexing manner for 8 ports. The number of CSI-RS ports and their resource positions are configured independently for each user. Thus, for different users, different resource positions may be occupied. Each user may further be configured with zero-power CSI-RS resources which are configured following the configuration of 4 CSI-RS ports. No signal is transmitted on the zero-power CSI-RS resources. The zero-power CSI-RS is configured via radio resource control (RRC) signaling. If a 4 port CSI-RS pattern is configured to be zero-power CSI-RS, it indicates that the user regards that no physical downlink shared channel (PDSCH) data is transmitted on these REs.
It can be seen from FIGS. 3a, 3b and 3c that, in one physical resource block (PRB) pair, the size of resources available for transmitting control channel varies with the CSI-RS configuration.
In LTE Rel-11 edition, enhanced PDCCH (ePDCCH) is transmitted in the PDSCH area (i.e., data area). For different CSI-RS configurations, the number of available REs in the PDSCH area may be different, i.e., the number of REs used for transmitting the ePDCCH is different, which has a relatively large impact to demodulation performance of control signaling.
At present, with respect to the LTE Rel-11 edition, there is no transmission solution for the ePDCCH.